Root surface caries affects a significant proportion of the aging adult population, and its incidence is on the raise. The etiology of this disease unclear, however some bacteria are isolated from root caries lesions most often: Lactobacilli, Streptococcus mutans and Actinomyces. The mechanisms which localize these and other bacteria to the root surface are unknown and therefore effective means of treating root surface caries are poorly developed. We propose that bacteria which are implicated, directly or indirectly, in the etiology of root surface caries, attach to the tissue via specific interactions involving bacterial adhesins on one side and components of the dentin on the other. We will study the interactions of bacteria with the major components of dentin - collagen type I, proteoglycans and phosphophoryn. Fresh clinical isolates of bacteria will be screened for the ability to recognize these ligands, and any interactions will be characterized. We will determine if the expression of particular receptors correlates with the ability of the strain to attach to ligand coated surfaces, or pieces of dentin. Several potential inhibitors of these interactions will be considered - ligands, ligand analogues or fragments, and antibodies against bacterial surface components. Our observations may facilitate future studies on the prevention and treatment of root surface caries, involving not only procedures which kill bacteria (fluoridation, antibacterial dentifrices) but also those which specifically prevent colonization of the tissue by pathogenic species.